A contactless card or proximity card is a specific type of integrated circuit card (“IC card”), namely, a contactless integrated circuit device that can receive an input which is processed and subsequently delivered as an output. Proximity cards operate on the basis of communication by an electromagnetic field with a read and/or write interrogating device, generically referred to as a reader.
In proximity card applications, the reader typically transmits a carrier signal which creates an electromagnetic field. This carrier signal can serve on the one hand to power the contactless card, which is derived by converting the electromagnetic field into a DC voltage, and on the other hand to initiate a communication between the card and the reader. Both the contactless card and the reader of such applications each employ a demodulator to recover the information content from the carrier signal. Established communication protocols between the reader and the contactless card have been defined, for example, by ISO (International Organization for Standardization) 14443, Type A/B/C.
Conventional demodulators that are being used by both contactless cards and readers in these types of applications are fully analog circuit structures. As a result, the performance of the demodulator circuit is dependent on temperature as well as technology variances. Additionally, these analog circuit implementations make it difficult for system designers to apply even small concept changes to the applications.